Tube temperature indicator



p 1936. G. A. DAVIDSON TUBE TEMPRATURE INDICATOR Fild Oct. 8, 1954 InVentof George A. Dawbson as those used for liquid cal temperature of about Patented Sept. 22, 1936 PATENT OFFICE TUBE rammam: nm rcrn George A. Da vidson,

E1 Segundo, CaliL, assigner to Standard Oil Company of California, San

Franeiseo, Calit., a corporation o! Delaware Application October 8,1934, Serial No. 747,482 Claims. (CL,I332i This invention relates to a temperature measurmg device,and'particulafly to one adapted'to be used in connection with the metal tubes in an oii heating turnace, to give a positive and visual indication of the operating temperature of the said tubes.

In the operation of tubular oil heaters, such phase cracking of petroleum, it is very essential that the temperatare of the tubes be kept below certain limits, to prevent excessive decomposition'of thefluid in the tube With result.nt coke and gas formation. Another and more important factor is that of the physical condition of the metal of the tube, particularly where the non-corrosive alloys, such as chromium-nickel-iron, are utilized. Certain of these are quite strong, tough and ductile so long as they are not overheated, but have a criti- 1200 F., at which they lose their strength and become weak and brittle.

Inasmuch as the tubes in such a heater may be operating full of oil and gas and at pres- 'sures up to 1000 pounds per square inch. a tube ial1ure due to anynause may result in a serious flre or explosion, that will not only jeopardize the safety of the operators but may destroy valuable equipment.

Heretoiore, various expedients for determining tube operating temperatures have been tried, such as thermocouples welded to the tube wall, optical pyrometers, etc. The thermocouples require an elaborate and expensive system of wiring and delicate electrical instruments and are Subject to rapid deterioration and burning off during long runs, leaving the operator with no guidance whatever as to tube Wai1 conditions. Furthermore the relatively thin lead wires are easily damaged during,cleaning periods, from vibrations set up by tuba cleaners, repairs to refractory walls, and the like. Optical pyrometers are adversely afiected and rendered inaccurate by the hot gases in the iurnace chamber, the radiation from the retractory walls, etc., and are of little value in indicating the true temperature of the tube walls in this type of service.

'Ihis invention, however, depends upon the change of color due to the temperature of heated metal studs or pegs, attached at intervals along the tubes, asby being welded thereto, and which are visually observed by the fireman' or operator as hequenflyyas may be desired. They involv no wiring or supplementary instruments, are readily and economically installed and removed, and have proved to be quite rugged, simple and reliable guides as to the temperature of the tubes,

thus permitting them 'to be operated et maximum eiflcienc and with a minimum likelihood of fail- It is an object of this'invention to provide a simple and economical means for indicating safe maximum temperatvregot. tube walls oi. tubular heaters,'such as liqid' phase pressure stills.

Another object is to provide a means for visually determining the temperature gradient along a given tube as may be caused by localized carbon or coke deposition therein, which may intertere with the transmission of heat through the tube to the fluid passing through the same, and cause the tube to be overheated at that point, while adjacent areas are at safe operating temperatures.

Another object is to provide a means for eccnomically indicating sure still tube at a pluraiity et points, which means may readily and cheapiy be installed and repla.ced, and which will not require either expensive supplementary apparatus, continuous maintenance, or expert manipulation.

These and other objects and advantages will become further apparent from the following description, and from the accompanying drawing, which forms a part of this specification and illustrates a preferred embodiment of this invention, together With several alternative forms thefeof.

In the drawing, Figure 1 is a transverse sectional viewof a pressure still tube with a number of temperature indicating studs or pegs welded thereto.

Figure 2 isa side elevation view of a portion of a pressure still tube with a plurality of pegs welded to its outer surface.

Figure 3 is a sectional view similar to Figure 1 and shows an alternative form of the studs.

Figure 4 is also a transverse sectional view of a tube with a simpler and still diierent form of temperature indicating studs, in which the diameter is constant throughout.

Referring to the drawing, and particularly to Figures 1 and 2, the numeral I0 represents the tube to which the studs or pegs Il are attached, as by weiding at their bases l2. Each stud Il is preferably pr0gressively reduced in diameter from the base l2 to the tip [3, as by steps M and l5. If desired, the reduction in cross-sectional area may be uniform as from base l2 to tip la of the stud II of Figure 3. It has also been iound that a simple cylindricai stud as shown et II" of Figure 4, will give quite satisfactory results, as will be explained below.

Studs Il may be welded, as shown in Figure 2, at the desired intervais along those tubes most the temperature of a presexposed to the heat, and particularly the radiant heat of a pressure still furnace, and are preferably so positioned that they are visible throughout their length fromthe observation ports or peep-holes common to such furnaces. Both the tube l and pegs Il are in heat absorptive relatian to the hot gases and/or radiating surfaces in the furnace Due to the relatively larger area of the body of the peg which is exposed to the absorption of heat as compared to the area at the base l2 through which the heat is being carried away to the tube l0, the peg will be at a higher temperature than the tube. The tip l3 of the peg Il will obviously attain the highest temperature and will, therefore, become red hot before the rest of the peg or the tube.

The apparent color of such a peg and the tube to which it may be attached will depend on several factors. In a furnace with a bright high fire the appearance of a red hot or souri-incandescent body will be difierent than when a low or non-luminous fire is carried. Thematerials of the tubes and the pegs also affect the appearance. Carbon steel tubes have a difierent color when at or near a ted heat than the corrosionresisting alloy tubes such as chromium-niekeliron, probably due to the oxide films thereon. Preierably the pegs Il are of the same material as the tube Il), and it will be found that a quite noticeable difierence in appearance will be observed between the red or semi-incandescent tip l3 of the peg Il and the normal color of the tube l0.

As the temperature of the tube increases and approaches redness, which may indicate the critical temperature, less heat is absorbed from the body of peg H, and the different color of the peg will extend doser to the tube, until the tube temperature apprqximates 1200 F., when the distinctive appearance or color of the peg will have reached the junction point or base l2. From this indication it is very easy to detect a tube or any portion of a tube which is Operating above the desired maximum, by a simple visual observation of the peg colors.

In one application, where the critical point below which the tube wall temperature was to be kept was about 1200 F., the studs Il were in diameter at the base and A" in diameter at the tip, when made in the stepped forms of Figures 1 and 2, and were about 2 inches in length.

Simple cylindrical forms such as that of Figure 4;

of diameter and 2" length, were also found to operate satisfactorily.

If the taper were uniform, as in Figure 3, a base diameter of and a tip diameter of /3", With a length of 2 inches, was found suitable. These varying sizes show that the dimensions are not particularly critical, and may be varied as found advantageous. Consideration of these proportiens, however, will show that the mean diameter is preferably one-tourth or less of the length, the range shown being about one-fourth to about one-eighth.

Although a specific construction embodying this invention has been described and illustrated, it is to be understood that the invention is not limited to that specific device, and all such modifications and changes as come Within the scope of the appended claims are embraced thereby.

I claim:

1. In apparatus for heating a fluid such as oil, a metal tube in which said fluid is to be heated, and a metal peg secured to the outer surface of said tube, the mean diameter of said peg being about one-fourth to about one-eighth of its length, so that a considerable temperature gradient is maintained along said peg and the amount or length of glow of said peg is indicative et the temperature of said tube.

2. An apparatus according to claim 1, in which the juncture of said peg with said tube is of larger cross-sectional area than the tip of said peg.

3. An apparatus according to claim 1, in which the juncture of said peg with said tube is of larger cross-sectional area than the tip of said peg, the reduction being uniform throughout the length of said peg.

4. An apparatus according to claim 1, in which said peg is progressively reduced in diameter from its base to its outer end.

5. A pressure still tube to which is secured one or more outwardly projecting metal pegs, the mean diameter thereof bains about one-fourth to about one-eighth of the length, and so constructed and arranged relative to the tube and the operating temperature thereof that a considerable temperature gradient along said peg or pegs is maintained and the amount and length of glow of said peg or pegs 1s indicative of the temperature of said pressure still tube.

GEORGE A. DAVIDSON. 

